Create 2025-01-14-Leetcode-71.md

_posts/2025-01-14-Leetcode-71.md

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+---
+title: Leetcode 71. Simplify Path
+description: Explanation for Leetcode 71 - Simplify Path, and its solution in Python.
+date: 2025-01-14
+categories: [Leetcode, Stack, Medium]
+tags: [Leetcode, Python, Study, Stack, Medium]
+math: true
+---
+
+## Problem
+[Leetcode 71 - Simplify Path](https://leetcode.com/problems/simplify-path/description/)
+
+Example:
+```
+Input: path = "/home/"
+Output: "/home"
+Explanation: The trailing slash should be removed.
+
+Input: path = "/home//foo/"
+Output: "/home/foo"
+Explanation: Multiple consecutive slashes are replaced by a single one.
+
+Input: path = "/home/user/Documents/../Pictures"
+Output: "/home/user/Pictures"
+Explanation: A double period ".." refers to the directory up a level (the parent directory).
+
+Input: path = "/../"
+Output: "/"
+Explanation: Going one level up from the root directory is not possible.
+
+Input: path = "/.../a/../b/c/../d/./"
+Output: "/.../b/d"
+Explanation: "..." is a valid name for a directory in this problem.
+```
+
+## Approach
+
+As explained in the description of the problem,
+
+- a single period '.' represents the current directory
+    - we can just ignore when we encounter '.'
+- a double period '..' represents the previous/parent directory
+    - we can pop the stack if len(stack) > 0 
+- multiple consecutive slashes such as '//' or '///' are treated as single slash '/'
+    - we can ignore this since .split('/') will solve this 
+- any sequence of periods that does not match the rules above should be treated as a valid directory or file name.
+    - append it to stack
+
+When this is all done, we can join the stack with '/'. Since we must also start with '/' for return value, we have to add '/'
+
+Visualization of the Approach:
+```
+path = "/home/user/Documents/../Pictures"
+
+After doing split operation
+path = ['', 'home', 'user', 'Documents', '..', 'Pictures']
+stack = []
+
+Since '' is empty, we ignore and continue
+stack = []
+
+Since 'home' is a valid name for directory add it to stack
+stack = ['home']
+
+Since 'user' is a valid name for directory add it to stack
+stack = ['home', 'user']
+
+Since 'Documents' is a valid name for directory add it to stack
+stack = ['home', 'user', 'Documents']
+
+Since '..', we should pop one from stack if len(stack) > 0
+stack = ['home', 'user']
+
+Since 'Pictures' is a valid name for directory add it to stack
+stack = ['home', 'user', 'Pictures']
+
+When we return we must add '/' first then join the list with '/'
+Thus, res = '/home/user/Pictures'
+```
+
+Here is the Python code for the solution:
+```python
+class Solution:
+    def simplifyPath(self, path: str) -> str:
+        stack = []
+        path = path.split('/')
+
+        for p in path:
+            if p == '':
+                continue
+            elif p == '.':
+                continue
+            elif p == '..':
+                if len(stack) == 0:
+                    continue
+                else:
+                    stack.pop()
+            else:
+                stack.append(p)
+
+        return '/' + '/'.join(stack)
+```
+## Time Complexity and Space Complexity
+
+Time Complexity: $O(n)$
+
+Space Complexity: $O(n)$